The present invention relates to a heat pump apparatus incorporating a compression type refrigerating circuit and, more particularly, to a heat pump apparatus having a plurality of compressors and heating condensers connected to the compressors.
Various problems are encountered in the generation of hot water or hot air by a heat pump apparatus incorporating a compression type refrigeration circuit. For example instance, the coefficient of performance of the compressor is reduced due to a large pressure difference between the high-pressure side and low-pressure side of the refrigeration circuit. Moreover, the temperature of the refrigerant gas discharged from the compresor is often raised abnormally to a level above the decomposition temperature of the refrigerant.
In, for example, Laid-Open Patent Applications Nos. 114033/75, 118342/75 and 29934/72, an apparatus for generating high temperature is proposed wherein a compression type refrigeration circuit is used as a heat pump. Additionally, in, for example, Japanese Laid-Open Patent Applications 114033/75 and 118342/75, a warm water generating apparatus is associated with air conditioner, in which a condenser for generating warm water is provided at the discharge side of the compressor separately from the condenser for air conditioner so that warm water is generated by the superheated temperature component of the refrigerant gas discharged from the compressor. Usually, the air conditioner is operated at a comparatively low temperature range, e.g. 50.degree. C. in terms of condensation temperature, in order to avoid various troubles such as damaging of compressor by heat and thermal decomposition of the refrigerant and the lubricant. In this warm water generating system, however, the heat of the superheated temperature component is comparatively small and the temperature level of this heat is rather low. Therefore, additional heating by an auxiliary electric heater or boiler is essential for obtaining a large amount of warm water or warm water of a high temperature level.
In aforementioned Japanese Laid-Open Application No. 29934/72 a system for generating hot water utilizes two heat pump type refrigeration circuits. Namely, warm water generated in the condenser of the heat pump type refrigeration circuit operating at lower temperature is utilized as the heat source of the heat pump type refrigeration circuit operating at higher temperature, so that a condensation temperature, considerably higher than that of the first refrigeration circuit, is attained in the second refrigeration circuit to permit the generation of warm water of high temperature. The refrigeration circuit operating at higher temperature makes use of a refrigerant the vapor pressure of which is not so high even at a high temperature. It is, therefore, possible to obtain warm water of high temperature well reaching 80.degree. C. This system, however, suffers from a problem that the coefficient of performance is considerably low as compared with other systems incorporating only one refrigeration circuit.
Systems pertinent to the invention of this application, incorporating multi-stage compressor or a plurality of compressors and receivers, are disclosed in Japanese Utility Model Laid-Open Applications Nos. 78849/74 and 60754/79; however, these systems do not make use of the heat medium of high temperature but a heat medium of low temperature cooled by evaporator.
More specifically, in the system disclosed in Laid-Open Application 78849/74, a compound compressor having two stages is provided, with the refrigerant gas, discharged from the compressor of low pressure stage being introduced into a receiver where it merges in the liquid refrigerant condensed in the condenser of the high pressure stage to form an almost saturated refrigerant gas which is drawn in by the compressor of the high pressure stage. The heat taken from the heat medium of lower temperature in the evaporator of the low pressure stage is delivered to the outside through the condenser of the high pressure stage. There is no heat exchanging relationship between the outside and the intermediate pressure section connected to the discharge side of the compressor of low pressure stage. Namely, in the intermediate pressure section, the heat is exchanged only between the refrigerant fractions in the refrigeration system, i.e. only between the refrigerent gas of high temperature discharged from the compressor of high low pressure stage and the liquid refrigerant in the high pressure stage. When this system is used for generating a heat medium of high temperature, the coefficient of performance is inevitably low as compared with a single-stage refrigeration system, because the system operating in two stages cannot produce heat greater than that produced by the single-stage refrigeration system, due to inability to use the heat possessed by the refrigerant gas discharged from the compressor of the low pressure stage. However, in this system, problems, such as, for example, damaging of compressor by excessive heat and thermal decomposition of lubricant and refrigerant, are avoided due to a comparatively low temperature of the gas discharged from the compressor of high pressure stage because the latter draws almost saturated refrigerant gas.
The system in Japanese Utility Model Laid-Open Application No. 60754/79 differs from that shown in Laid-Open Application No. 78849 only in that this system incorporates two compressors and the gas, discharged from the compressor of the low pressure side, does not merge in the liquid refrigerant in the high presure side but makes a heat exchange with the latter.
Accordingly, it is an object of the invention to provide a heat pump apparatus incorporating a compression type refrigeration circuit having a high operation efficiency, capable of delivering air or water of high temperature.
Another object of the invention is to provide a heat pump apparatus which can permit a selection of the temperature range of warm water or air and, hence, deliver warm air or water of desired temperature level.
Still another object of the invention is to provide a heat pump apparatus which can generate not only warm air or water but also a heat medium of low temperature such as cold air or water.
A further object of the invention is to provide a heat pump apparatus which can effectively be applied to an air conditioner.
To these ends, according to the invention, a heat pump apparatus is provided which comprises a main refrigerant circuit having a compressor, condenser, gas-liquid separator, a presure reducing means (expansion valve) and an evaporator which are connected to form a closed loop, and an auxiliary refrigerant line shunting from the gaseous phase portion of the gas-liquid separator and leading to the evaporator through a compressor, condenser, and a pressure reducing means which are provided separately from those of the main refrigerant circuit.
In operation, the gaseous refrigerant of high temperature and pressure, discharged from the compressor, is introduced into the condenser to heat a heat output medium such as water, air or the like circulated through the condenser. As a result of this heat exchange, the refrigerant itself is condensed into liquid and then flows into the gas-liquid separator where the gaseous phase of the refrigerant is separated from the liquid phase. The liquid refrigerant then flows through the presure reducing means (expansion valve) into the evaporator where the refrigerant is evaporated through a heat exchange with an external heat source. The evaporated through a heat exchange with an external heat source. The evaporated refrigerant is returned to the suction side of the compressor.
On the other hand, the gaseous refrigerant, which is in saturated state and accumulated in the upper part of the gas-liquid separator, is introduced to and compressed by the compressor of the shunting refrigerant line. The gaseous refrigerant of high temperature and pressure discharged from the compressor is introduced into the condenser of the shunting refrigerant line and is condensed at a temperature higher than the condensation temperature in the main refrigerant circuit, while additionally heating the heat output medium which has been heated in the condenser of the main refrigerant circuit. Alternatively, the condensation in the condenser of the shunting refrigerant line is accomplished by the heat derived from another heat output medium so that heat output mediums of different temperatures are served by the heat pump apparatus as a whole. It is also possible to use a non-azeotropic refrigerant mixture and, in such a case, most of the refrigerant component having higher boiling point is condensed in the condenser of the main refrigerant circuit, while the refrigerant component of lower boiling point is separated in gaseous phase within the gas-liquid separator. This gaseous refrigerant is introduced into the condenser of the shunting refrigerant lines and is condensed at a temperature higher than the condensation temperature of the main refrigerant circuit, while additionally heating the heat output medium to a higher temperature.
According to the invention, it is possible to increase the number of the shunting refrigerant lines in compliance with the demand for different temperature levels of the heat output medium, Namely, it is possible to obtain desired temperature levels corresponding in number to the number of the shunting refrigerant lines.
When a plurality of shunting refrigerant lines are incorporated, it is possible to obtain a higher temperature of the output heat medium by using a nonazeotropic refrigerant consisting of three components of high, low and medium boiling temperature and by arranging the same such that these components are condensed in the condenser of the main refrigerant circuit, condenser of the first shunting refrigerant line and the condenser of the second shunting refrigerant line, respectively.
Thus, in the heat pump apparatus of the invention, the compressor of the shunting refrigerant line draws almost saturated gaseous refrigerant separated by the gas-liquid separator and discharges the compressed gaseous refrigerant at a temperature which is sufficiently lower than the decomposition temperature of the refrigerant which materially limits the range of operation of the heat pump apparatus. Therefore, the condensation temperature in the shunting refrigerant line can be elevated to a level higher than that in the refrigeration circuit having a single compressor, i.e. refrigerant circuit having a single compression stage, which in turn permits the generation of higher temperature of the heat output medium such as water and air. In addition, the efficiency of the heat pump apparatus as as whole as remarkably improved because it is not necessary to compress the whole part of the refrigerant to high condensation pressure.
It is of course possible to obtain a heat medium of low temperature in the evaporator of the heat pump apparatus of the invention. In a preferred form in which each shunting refrigerant line has an evaporator, it is possible to independently cool heat media in the respective evaporators or, alternatively, to cool a heat medium first in the evaporator of high evaporation temperature through a heat exchange with a refrigerant components of higher boiling point and then in another evaporator of lower evaporation temperature through a heat exchange with the refrigerant component of lower boiling point. In the latter case, it is possible to obtain a heat medium of a lower temperature.
In another preferred form, the gas-liquid separator is provided with a heater whereby it is possible to control the capacity of the heat pump apparatus in three stages by suitably selecting one of three operation modes: namely, a first mode in which only the main refrigerant circuit operates, a second mode in which only the shunting refrigerant line operates and a third mode in which both of the main refrigerant circuit and the shunting refrigerant line operates.
According to still another preferred form, the heat pump apparatus is provided with a four-way valve for switching the flow of the refrigerant, an expansion valve for heating, an expansion valve for cooling and check valves disposed in respective expansion valves, so that the heat pump apparatus can operate selectively either in heating mode or cooling mode. With this arrangement, it is possible to attain a greater heating capacity and, hence, a higher temperature of heated air, while, in the cooling mode, only the main refrigeration circuit operates. Thus, the heat pump apparatus of this arrangement can be used as an air conditioner suited for use in cold district where the heating load or demand is much greater than the cooling load or demand.
These and other objects, features and advantages of the invention will become clear from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.